1. Field of the Disclosure
The present disclosure relates generally to fusers used in electrophotographic image forming devices and more particularly to an externally heater fuser assembly for variable sized media.
2. Description of the Related Art
In an externally heated fuser assembly for an electrophotographic image forming device, a heating lamp radiates heat onto the outer surface of a fusing roll or belt. The heated fusing roll or belt is pressed against a backup roll or belt forming a fusing nip. The heating lamp extends the full width of the printing process in order to suitably heat and fuse toner to the widest media sheets used with the image forming device. The fusing heat is controlled by measuring the temperature of the fusing roll or belt and feeding the temperature information to a microprocessor-controlled power supply in the image forming device. The power supply applies power to the heating lamp when the temperature sensed drops below a first predetermined level and interrupts power when the temperature exceeds a second predetermined level. In this way, the fuser assembly is maintained at temperature levels suitable for fusing toner to media sheets without overheating.
When printing, the media sheet removes heat from the fuser assembly in the portion of the fuser that contacts the media. When printing on media sheets having widths that are less than the widest media width on which the image forming device is capable of printing, the portion of the fuser assembly beyond the width of the media sheet does not lose heat through the sheet and becomes hotter than the portion of the fuser assembly that contacts the media sheet. In order to prevent thermal damage to components of the fuser assembly, steps are taken to limit the overheating of the portion of the fuser assembly that does not contact narrower media sheets. Typically, the inter-page gap between successive media sheets being printed is increased when media sheets less than the full width are used. However, increasing the inter-page gap between successive media sheets slows the process speed of the image forming device which may lead to customer dissatisfaction. Accordingly, an improved fuser assembly for use with printing on narrower media sheets is desired.